1. Field of the Invention
This invention relates to an apparatus for magnifying a display surface of an indicator, such as a meter or gauge, and forming an enlarged image of the display surface at a forward place distant from a driver and other passengers in a motor vehicle.
2. Description of the Prior Art
Conventionally, a display image magnifying apparatus for a vehicle is known as shown in FIG. 21. In FIG. 21, reference numeral 1 designates an indicator on which information given by a speedometer, a tachometer, a fuel gauge, and the like is displayed, reference numeral 2 designates a half mirror, and reference numeral 3 designates a concave mirror. A beam of light emitted from a display surface 1a of the indicator 1 passes through the half mirror 2 and reaches the concave mirror 3. An image of the display surface 1a enlarged by the concave mirror 3 is formed over the concave mirror 3 as a virtual image. Light from the image is reflected by the half mirror 2 and proceeds toward an eye point of the driver.
As a result of the reflection of the light by the half mirror 2, the image 1b of the display surface 1a is formed at a forward place distant from the driver. Since the image 1b viewed by the driver is enlarged and formed at the distant place, the image 1b is very easy for the driver to discern.
The size of each character in the image 1b is determined such that each character falls within a visual angle of the driver, and the size of the image 1b is determined such that the image 1b is viewed within an eye range of the driver and with both eyes of the driver.
However, in the conventional apparatus, an optical axis 5 is arranged to extend through the eye point of the driver. For this reason, when the image 1b of the display surface 1a is viewed from, for example, an assistant driver's seat (passenger seat) which Is a point other than the eye point of the driver, a direction in which the image 1b is viewed considerably deviates from the optical axis 5. In addition, a distance between the display surface 1a and the concave mirror 3 measured from the eye point of the driver is different from a distance therebetween measured from the assistant driver's seat. This causes distortion of the image 1b. The higher the magnifying power is, the worse the distortion of the image 1b becomes.
Generally, distortion of the image 1b in right and left directions can be corrected by brain action of a viewer so as not to feel a great difficulty in viewing, but distortion thereof in up and down directions cannot be corrected by the brain action and therefore the image 1b is very difficult to discern.
Another magnifying apparatus is known in which a cylindrical lens is disposed between an indicator 1 and a half mirror 2 so as to lower the magnifying power in up and down directions and heighten the magnifying power in right and left directions (see Japanese Patent Application Early Laid-Open Publication No. Hei 4-103437). However, this apparatus is constructed for a driver to easily and clearly view an image of the indicator 1. In the apparatus, no attention is paid to a case in which the image of the indicator 1 is viewed from an assistant driver's seat. For this reason, disadvantageously, the image is very difficult to discern when viewed from the assistant driver's seat.